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Date: Mon, 30 Jul 2012 11:20:37 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>
Subject: [PATCH] net: ipv4: fix RCU races on dst refcounts
From: Eric Dumazet <edumazet@...gle.com>
commit c6cffba4ffa2 (ipv4: Fix input route performance regression.)
added various fatal races with dst refcounts.
crashes happen on tcp workloads if routes are added/deleted at the same
time.
The dst_free() calls from free_fib_info_rcu() are clearly racy.
We need instead regular dst refcounting (dst_release()) and make
sure dst_release() is aware of RCU grace periods :
Add DST_RCU_FREE flag so that dst_release() respects an RCU grace period
before dst destruction for cached dst
Introduce a new inet_sk_rx_dst_set() helper, using atomic_inc_not_zero()
to make sure we dont increase a zero refcount (On a dst currently
waiting an rcu grace period before destruction)
rt_cache_route() must take a reference on the new cached route, and
release it if was not able to install it.
With this patch, my machines survive various benchmarks.
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
include/net/dst.h | 7 +------
include/net/inet_sock.h | 13 +++++++++++++
net/core/dst.c | 26 +++++++++++++++++++++-----
net/decnet/dn_route.c | 6 ++++++
net/ipv4/fib_semantics.c | 4 ++--
net/ipv4/route.c | 16 ++++------------
net/ipv4/tcp_input.c | 3 +--
net/ipv4/tcp_ipv4.c | 12 ++++++------
net/ipv4/tcp_minisocks.c | 3 +--
9 files changed, 55 insertions(+), 35 deletions(-)
diff --git a/include/net/dst.h b/include/net/dst.h
index baf5978..31a9fd3 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -61,6 +61,7 @@ struct dst_entry {
#define DST_NOPEER 0x0040
#define DST_FAKE_RTABLE 0x0080
#define DST_XFRM_TUNNEL 0x0100
+#define DST_RCU_FREE 0x0200
unsigned short pending_confirm;
@@ -382,12 +383,6 @@ static inline void dst_free(struct dst_entry *dst)
__dst_free(dst);
}
-static inline void dst_rcu_free(struct rcu_head *head)
-{
- struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
- dst_free(dst);
-}
-
static inline void dst_confirm(struct dst_entry *dst)
{
dst->pending_confirm = 1;
diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index 613cfa4..e3fd34c 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -249,4 +249,17 @@ static inline __u8 inet_sk_flowi_flags(const struct sock *sk)
return flags;
}
+static inline void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb)
+{
+ struct dst_entry *dst = skb_dst(skb);
+
+ if (atomic_inc_not_zero(&dst->__refcnt)) {
+ if (!(dst->flags & DST_RCU_FREE))
+ dst->flags |= DST_RCU_FREE;
+
+ sk->sk_rx_dst = dst;
+ inet_sk(sk)->rx_dst_ifindex = skb->skb_iif;
+ }
+}
+
#endif /* _INET_SOCK_H */
diff --git a/net/core/dst.c b/net/core/dst.c
index 069d51d..d9e33eb 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -258,6 +258,15 @@ again:
}
EXPORT_SYMBOL(dst_destroy);
+static void dst_rcu_destroy(struct rcu_head *head)
+{
+ struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
+
+ dst = dst_destroy(dst);
+ if (dst)
+ __dst_free(dst);
+}
+
void dst_release(struct dst_entry *dst)
{
if (dst) {
@@ -265,10 +274,14 @@ void dst_release(struct dst_entry *dst)
newrefcnt = atomic_dec_return(&dst->__refcnt);
WARN_ON(newrefcnt < 0);
- if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) {
- dst = dst_destroy(dst);
- if (dst)
- __dst_free(dst);
+ if (unlikely(dst->flags & (DST_NOCACHE | DST_RCU_FREE)) && !newrefcnt) {
+ if (dst->flags & DST_RCU_FREE) {
+ call_rcu_bh(&dst->rcu_head, dst_rcu_destroy);
+ } else {
+ dst = dst_destroy(dst);
+ if (dst)
+ __dst_free(dst);
+ }
}
}
}
@@ -320,11 +333,14 @@ EXPORT_SYMBOL(__dst_destroy_metrics_generic);
*/
void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
{
+ bool hold;
+
WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
/* If dst not in cache, we must take a reference, because
* dst_release() will destroy dst as soon as its refcount becomes zero
*/
- if (unlikely(dst->flags & DST_NOCACHE)) {
+ hold = (dst->flags & (DST_NOCACHE | DST_RCU_FREE)) == DST_NOCACHE;
+ if (unlikely(hold)) {
dst_hold(dst);
skb_dst_set(skb, dst);
} else {
diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index 85a3604..2671977 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -184,6 +184,12 @@ static __inline__ unsigned int dn_hash(__le16 src, __le16 dst)
return dn_rt_hash_mask & (unsigned int)tmp;
}
+static inline void dst_rcu_free(struct rcu_head *head)
+{
+ struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
+ dst_free(dst);
+}
+
static inline void dnrt_free(struct dn_route *rt)
{
call_rcu_bh(&rt->dst.rcu_head, dst_rcu_free);
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index da0cc2e..e55171f 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -172,9 +172,9 @@ static void free_fib_info_rcu(struct rcu_head *head)
if (nexthop_nh->nh_exceptions)
free_nh_exceptions(nexthop_nh);
if (nexthop_nh->nh_rth_output)
- dst_free(&nexthop_nh->nh_rth_output->dst);
+ dst_release(&nexthop_nh->nh_rth_output->dst);
if (nexthop_nh->nh_rth_input)
- dst_free(&nexthop_nh->nh_rth_input->dst);
+ dst_release(&nexthop_nh->nh_rth_input->dst);
} endfor_nexthops(fi);
release_net(fi->fib_net);
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index fc1a81c..d6eabcf 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1199,11 +1199,6 @@ restart:
fnhe->fnhe_stamp = jiffies;
}
-static inline void rt_free(struct rtable *rt)
-{
- call_rcu_bh(&rt->dst.rcu_head, dst_rcu_free);
-}
-
static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
{
struct rtable *orig, *prev, **p = &nh->nh_rth_output;
@@ -1213,17 +1208,14 @@ static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
orig = *p;
+ rt->dst.flags |= DST_RCU_FREE;
+ dst_hold(&rt->dst);
prev = cmpxchg(p, orig, rt);
if (prev == orig) {
if (orig)
- rt_free(orig);
+ dst_release(&orig->dst);
} else {
- /* Routes we intend to cache in the FIB nexthop have
- * the DST_NOCACHE bit clear. However, if we are
- * unsuccessful at storing this route into the cache
- * we really need to set it.
- */
- rt->dst.flags |= DST_NOCACHE;
+ dst_release(&rt->dst);
}
}
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a356e1f..9be30b0 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5604,8 +5604,7 @@ void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
tcp_set_state(sk, TCP_ESTABLISHED);
if (skb != NULL) {
- sk->sk_rx_dst = dst_clone(skb_dst(skb));
- inet_sk(sk)->rx_dst_ifindex = skb->skb_iif;
+ inet_sk_rx_dst_set(sk, skb);
security_inet_conn_established(sk, skb);
}
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 2fbd992..7f91e5a 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1617,19 +1617,19 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
#endif
if (sk->sk_state == TCP_ESTABLISHED) { /* Fast path */
+ struct dst_entry *dst = sk->sk_rx_dst;
+
sock_rps_save_rxhash(sk, skb);
- if (sk->sk_rx_dst) {
- struct dst_entry *dst = sk->sk_rx_dst;
+ if (dst) {
if (inet_sk(sk)->rx_dst_ifindex != skb->skb_iif ||
dst->ops->check(dst, 0) == NULL) {
dst_release(dst);
sk->sk_rx_dst = NULL;
}
}
- if (unlikely(sk->sk_rx_dst == NULL)) {
- sk->sk_rx_dst = dst_clone(skb_dst(skb));
- inet_sk(sk)->rx_dst_ifindex = skb->skb_iif;
- }
+ if (unlikely(sk->sk_rx_dst == NULL))
+ inet_sk_rx_dst_set(sk, skb);
+
if (tcp_rcv_established(sk, skb, tcp_hdr(skb), skb->len)) {
rsk = sk;
goto reset;
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 3f1cc20..232a90c 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -387,8 +387,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
struct tcp_sock *oldtp = tcp_sk(sk);
struct tcp_cookie_values *oldcvp = oldtp->cookie_values;
- newsk->sk_rx_dst = dst_clone(skb_dst(skb));
- inet_sk(newsk)->rx_dst_ifindex = skb->skb_iif;
+ inet_sk_rx_dst_set(newsk, skb);
/* TCP Cookie Transactions require space for the cookie pair,
* as it differs for each connection. There is no need to
--
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